Self-test system

Abstract

An electronic system comprising a system to be monitored ( 2 ) and a plurality of fault-monitoring systems ( 4, 6 ) each of which is adapted to output a fault signal when an input indicates that the electronic system is in a fault condition associated with the fault-monitoring system. The fault-monitoring systems are arranged in a cascade fashion such that a fault signal output from one fault-monitoring system ( 4 ) is provided as an input to a subsequent fault-monitoring system ( 6 ) in the cascade of fault-monitoring systems to simulate a fault condition associated with the subsequent fault-monitoring system. The output of the final fault-monitoring system in the cascade gives an indication of whether there is a fault with any of the fault-monitoring systems.

1. An electronic system comprising a system to be monitored having a plurality of output signals, a plurality of fault-monitoring devices each of which is adapted to have a respective first input from the system to be monitored and an output for outputting a fault signal when a respective first input indicates that the system to be monitored is in a fault condition, wherein:
 the fault-monitoring devices are arranged in a cascade fashion, a fault-monitoring device having a second input connected to the output of a preceding fault-monitoring device; 
 the electronic system being adapted to induce a fault-monitoring device of the cascade to output a fault signal, which signal is cascaded as an input to the second input of a subsequent fault-monitoring device; 
 the electronic system being arranged to determine whether there is a fault with a fault- monitoring device by being arranged to create a record of a fault from the output of the final fault-monitoring device, the absence of a record being created when the electronic system induces a fault signal output signifying a fault in one of the fault-monitoring devices; 
 wherein a first fault-monitoring device is adapted to output a fault signal when the electronic system is placed into a switched-off condition; and 
 wherein the electronic system is associated with a vehicle and the electronic system is placed into a switched-off condition by turning an ignition key. 
 
   
   
     2. An electronic system according to  claim 1 , the electronic system further being arranged to:
 place the electronic system into a first fault condition and monitor for a generation of a first fault signal from a first fault-monitoring device, 
 on the generation of a first fault signal from the fault-monitoring device after placing the electronic system into a first fault condition, to input the first fault signal to the second fault-monitoring device, and 
 in response to an output from a final fault-monitoring device to store a record to this effect in non-volatile memory. 
 
   
   
     3. An electronic system according to  claim 2  wherein, on subsequent reversion of the electronic system to a non-fault condition, the electronic system is arranged to check whether the non-volatile memory includes a record and when the non-volatile memory does not include a record on a subsequent reversion, generate an alarm signal. 
   
   
     4. An electronic system according to  claim 1  wherein the first fault-monitoring device is a watch-dog system. 
   
   
     5. An electronic system according to  claim 1  wherein a second fault-monitoring device has as an input the fault signal from the first fault-monitoring device, the second fault-monitoring system being adapted to output a fault signal when the electronic system experiences an under- or over-voltage condition. 
   
   
     6. An electronic system according to  claim 1  further comprising storing a record of a fault signal output by any of the fault-monitoring devices to enable identification of a defective fault-monitoring device. 
   
   
     7. A self-test method for an electronic system comprising a system to be monitored having a plurality of output signals, a plurality of fault-monitoring devices each of which is adapted to have a respective first input from the system to be monitored and an output for outputting a fault signal when a respective first input indicates that the system to be monitored is in a fault condition, the fault-monitoring devices being arranged in a cascade fashion, each fault monitoring device having a second input connected to the output of a preceding fault-monitoring device, the electronic system being adapted to induce a fault monitoring device of the cascade to output a fault signal, which signal is cascaded as an input to the second input of a subsequent fault-monitoring device, the method comprising:
 inputting the fault signal from one fault-monitoring device to a subsequent fault-monitoring device to simulate a fault condition associated with the subsequent fault-monitoring device, wherein the output of a final fault-monitoring device in the cascade is used as an indicator of a fault in one of the fault-monitoring devices; 
 arranging the electronic system to determine whether there is a fault with a fault-monitoring device by being arranged to create a record of a fault from the output of the final fault-monitoring device, the absence of a record being created when the electronic system induces a fault signal output signifying a fault in one of the fault-monitoring devices; 
 adapting a first fault-monitoring device to output a fault signal when the electronic system is placed into a switched-off condition; and 
 placing the electronic system associated with a vehicle and the electronic system into a switched-off condition by turning an ignition key. 
 
   
   
     8. A self-test method according to  claim 7 , further comprising:
 placing the electronic system into a first fault condition and monitoring for a generation of a first fault signal from a first fault-monitoring device, 
 on the generation of a first fault signal from the fault-monitoring device after placing the electronic system into a first fault condition, inputting the first fault signal to the second fault-monitoring device, and 
 in response to an output from a final fault-monitoring device storing a record to this effect in non-volatile memory. 
 
   
   
     9. A self-test method according to  claim 8  further comprising, on subsequent reversion of the electronic system to a non-fault condition, checking whether the non-volatile memory includes a record and when the non-volatile memory does not include a record on subsequent reversion, generating an alarm signal. 
   
   
     10. A self-test method according to  claim 7  wherein the first fault-monitoring device is a watch-dog system. 
   
   
     11. An electronic system according to  claim 7  wherein a second fault-monitoring device has as an input the fault signal from the first fault-monitoring device, the second fault-monitoring system being adapted to output a fault signal when the electronic system experiences an under- or over-voltage condition. 
   
   
     12. A self-test method according to  claim 7  further comprising storing a record of a fault signal output by any of the fault-monitoring devices to enable identification of a defective fault-monitoring device.